1. Field of the Invention
The present invention relates to an image recording apparatus such as a copying machine, a printer, etc., and more specifically to an image recording apparatus having a conveying mechanism for conveying a recording medium such as cutting sheets of paper etc.
2. Description of the Related Art
Generally, an image recording apparatus such as an ink jet printer etc. conveys a recording medium supplied from a recording medium storage unit such as a paper feed cassette etc. to an image recording unit, and performs a recording process (records data). The conveying posture (skew) of a conveyed recording medium is corrected immediately before it is conveyed to the image recording unit.
If the recording medium obliquely travels and is conveyed to the image recording unit, record data is obliquely recorded on the recording medium. Additionally, in a color recording process, color displacements etc. occur. Thus, if the recording medium obliquely travels when it is conveyed, the quality of an image is degraded.
As a technique to solve the above-mentioned problem, for example, a patent document (Japanese Published Patent Application No. H11-268843) discloses the configuration of a sheet conveying device which includes a first conveying device, a second conveying device for conveying a sheet conveyed by the first conveying device and further conveyed downstream, and is capable of adjusting the angle made by the conveying direction by the first conveying device and the conveying direction by the second conveying device.
The sheet conveying device described in the patent document is realized by including an adjustment mechanism for allowing the direction of a resist roller to coincide with the travel direction of a transfer belt sliding on an image bearing member in the image recording unit.
The sheet conveying device according to the above-mentioned patent document includes the first conveying device configured by a movable side plate 155, a resist driving roller 153 supported for rotation on the movable side plate 155, a resist driven roller 154, a rack gear 156 provided for the movable side plate 155, a pinion gear 157 engaging with the rack gear 156, a stepping motor (M) 152 having the pinion gear 157 for a rotation shaft, and a microprocessor (MP) 151 for controlling the stepping motor (M) 152 as shown in FIG. 1.
The sheet conveying device according to the above-mentioned patent document further includes between the first conveying device and the second conveying device in the conveying path of a sheet P (recording medium): a touch plate 158 for touching the sheet P looped after fed by the first conveying device; two reflective sensors 159f and 159r that are provided separate from each other in the width direction of the sheet P downstream the touch plate 158, and detect the sheet P that loops at the height h. A detection signal of the reflective sensors 159f and 159r is configured to be processed by the microprocessor (MP) 151.
Furthermore, the sheet conveying device according to the patent document has the second conveying device configured by a transfer belt 163, a pincer roller 162 for moving a sheet P placed on the transfer belt 163 to slide on an image bearing member 161 (only one of the four image bearing members are shown in FIG. 1); transfer belt rollers 164 and 165 (only two driven rollers are shown in FIG. 1) on which the transfer belt 163 is looped over as movable.
Thus, in the sheet conveying device with the above-mentioned configuration according to the above-mentioned patent document, the microprocessor (MP) 151 controls the stepping motor (M) 152 such that the difference α between the loop height hf of the sheet P detected by the reflective sensor 159f and the loop height hr of the sheet P detected by the reflective sensor 159r can be canceled. That is, the microprocessor (MP) 151 corrects the skew of the sheet P by performing control such that the conveying direction of the sheet P by the first conveying device can match the conveying direction of the sheet P by the second conveying device.